The present invention relates generally to enhancing the flowability of particulate lime and more particularly to treatment of lime with effective amounts of selected fluid polymethylhydrogensiloxanes, polydimethylsiloxanes and/or mixtures thereof.
Limestone is a generic term designating rock comprising carbonate forms of calcium and magnesium (CaCO.sub.3 and MgCO.sub.3) along with varying percentages of impurities. Limestone is generally classified into three types on the basis of magnesium carbonate content: (1) "high-calcium" having no more than 5% MgCO.sub.3 ; (2) "magnesian" having 5-20% MgCO.sub.3 ; and (3) "dolomitic" having from 20-45.6% MgCO.sub.3. When subjected to high temperature kilning, limestone decomposes chemically into calcium oxide (CaO) and magnesium oxide (MgO) with the expulsion of carbon dioxide. This primary product, known as "quicklime", may be hydrated or slaked into "hydrated lime". Limes, including quicklime and hydrated lime, calcined from the above-noted limestone types are accordingly designated as high calcium, magnesian and dolomitic limes. Limes are also characterized as "vertical kiln", "calcimatic", and "rotary" on the basis of apparatus employed in kilning.
Quicklime and hydrated lime are susceptible to a great variety of uses, including, for example, use in refractory processes, flux and steel manufacture, pulp and paper manufacture, water treatment, glass making, non-ferrous metallurgical processing, waste treatment, petroleum refining and the like. See, generally, Kirk-Othmer, "Encyclopedia of Chemical Technology" 2nd Ed. Volume 12, pp. 414-459 (John Wiley & Sons, New York, 1967).
Numerous prior patents are of interest to the background of the invention. U.S. Pat. No. 2,866,760 proposes the use of highly porous catalysts to effect polymerization (i.e. crosslinking) of polysiloxanes to provide a waterproof coating on the surface of particles. U.S. Pat. Nos. 3,009,775 and 3,174,825 disclose preparation of water insoluble iron cyanide crystals by treatment with liquid organopolysiloxanes and then propose that small quantities of such treated crystals may be added to sodium chloride so as to reduce the tendency toward caking of the salt. U.S. Pat. No. 3,980,593 discloses silanes as components of yet another iron cyanide treatment of salt. U.S. Pat. No. 3,930,062 discloses the usefulness of alkoxysilanes to enhance the flowability of porcelain enamel frits. Most recently, U.S. Pat. No. 4,007,050 discloses rendering metal oxides hydrophobic by means of fluidized bed treatment at high temperatures with combinations of polyorganosiloxanes and organohalosilanes. Once again, the prior art treatments are generally seen to involve costly reagents and catalysts as well as time-consuming, expensive processing.
There exists, therefore, an ongoing need in the art for improved methods for enhancing flowability of particulate materials, including lime, which methods involve use of relatively inexpensive quantities of treating materials and relatively fewer and simpler process steps.